Arginine and Skeletal Muscle

Abstract

Abstract Arginine (Arg) is a conditionally essential amino acid that plays key roles in nitrogen metabolism and ureagenesis, in cellular multiplication, in energy metabolism, and in endothelial function. In healthy adults, besides adaptation to its dietary supply, Arg homeostasis depends on its synthesis thanks to a gut–kidney cooperation and on its recycling from citrulline. If quantitatively its most important use is protein synthesis, qualitatively, its role as precursor of nitric oxide (°NO) and polyamines is crucial. Endothelial function is based on the synthesis of °NO by endothelial °NO synthase. It is therefore compromised when the availability of its substrate Arg decreases or when the activity of the enzyme decrease as insulin resistance develops. Arg supplementation would thus be beneficial in situations of endothelial dysfunction by increasing Arg availability or indirectly via Arg-induced improvement in insulin sensitivity. Moreover, Arg may also act by its effects on other component of the metabolic syndrome. Arg could thus improve muscle protein homeostasis first through this vascular effect and increased delivery of substrates and anabolic factor to the muscle. In addition, Arg is a direct activator of mammalian/mechanistic target of rapamycin key player in the response of muscle protein synthesis to anabolic stimulus. Here also, Arg supplementation does not seem to affect protein homeostasis in a healthy situation; however, in situations of insulin resistance, it may have a protective effect against muscle loss. Arg may play a role in the adaptation to exercise. While acute or chronic Arg administration has no effect on exercise performance in healthy subjects, it may increase maximal aerobic capacity in patients with cardiovascular diseases. Last Arg could be protective on muscle protein metabolism during stress-induced hypercatabolism. First, it could improve immune function and this in part supported by clinical studies. Second, it could act on tissue healing and muscle repair. Third, it could promote muscle protein anabolism either via an improvement in the secretion and action of growth factor or through a direct action on the muscle. Unfortunately, human data supporting these effects are lacking.